


One year later

by Darkburst87



Category: Undertale (Video Game)
Genre: Age Difference, Desk Sex, Ecto-Penis (Undertale), Ecto-Tongue (Undertale), Fluff and Smut, Lab assistant!Sans, M/M, Mutual Pining, PWP, Pre-Accident W. D. Gaster, Rimming, Romance, Some Plot, Tentacle Dick, this is just porn
Language: English
Status: Completed
Published: 2017-03-30
Updated: 2017-03-30
Packaged: 2018-10-12 19:42:40
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 946
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10498167
Author URL: https://archiveofourown.org/users/Darkburst87/pseuds/Darkburst87
Summary: Sans has a crush on the royal scientist.





	

**Author's Note:**

> So this is my first Undertale fanfic. Please let me know if you enjoyed reading this.

  
Sans couldn’t believe his luck. He should have been home from working at the lab at least an hour ago. He knew that Papyrus would be asking him why he was late.. again. No doubt he would be disappointed since this would cut into their together time which mainly consisted of watching anime and eating spaghetti. With a heavy sigh, Sans made sure that he had put away all of his equipment before he turned off the lights in his small personal laboratory which was located right across from his bosses own private lab/office. The young assistant raised his hand to knock on his bosses door to let him know he was heading home for the evening but before he could do that he felt a cold and heavy hand on his shoulder. The unexpected touch sent shivers all throughout his bones. He knew who it was before he got a chance to look behind him. 

“Gaster. I was just looking for you.” Sans said a bit loudly than how he would normally speak to the brilliant royal scientist. Sans turned around to face him, immediately picking up on how close the other man was. He was so close that the small skeleton could feel the others surprisingly warm breath on his neck.

“Sans do you remember what today is?”  
Gaster spoke with a calm and soothing tone of voice. Sans shook his head because he honestly didn’t know. “It’s the one year anniversary of when you became my assistant. I wanted to tell you this earlier today but I had just been so caught up in my work that I couldn’t.” Sans eyes went wide as the tall royal scientist conjured an extra pair of hands to open the door that Sans stood in front of. With his regular hands he pushed the somewhat frightened assistant inside. An extra hand closed and locked the door behind them.

“G-Gaster, sir…what is this all about?” Sans voice shook as he couldn’t help but notice how handsome his boss was and that his smile looked somewhat predatory. “You should know Sans that I notice everything. Did you honestly think that I didn’t catch on to the lingering looks you’ve given me over the past year?” Gaster reached out to cup the side of Sans face, slowly he ran his fingers across the smooth bone there before crashing his teeth to a startled Sans in a very heated skeleton kiss.  
Sans hesitated for about half a second before returning the kiss. He put everything he possibly could into the kiss, all of the words he never thought he would have ever been able to say out loud. Gaster moaned between kisses. Sans stepped back from him, in order to catch his breath. “I didn’t think you noticed that I want you more than someone ought to want their boss.”  
Gaster let out a low chuckle before closing the space between them once more, as he peeled off his young assistant’s lab coat from his shoulders, it dropped to the floor at their feet. Gaster ran his hands underneath Sans shirt, he ran his finger tips across his smooth bones. Sans placed his knee between Gaster’s legs. Gaster leaned into it, his arousal straining against the confines of his slacks. The older scientist let out a growl underneath his breath that turned Sans on even more. Eventually they made their way further into the room. 

  
Gaster had Sans bent over his desk, with his pants down and around his ankles. Gaster kissed Sans collarbone, slowly he worked his way lower. Sans moaned as he felt his bosses long conjured tongue enter the tight ring of muscle of his hole that he had secretly conjured earlier during their first kiss. Sans was so lost in the sensations and his own arousal that he had not registered the sound of Gaster unbuckling his slacks. “Do you need me to fuck you Sans?” His voice was husky and low, a rumble against the back of his skull. Sans shook his head and moaned loudly.  
“I’m sorry I didn’t hear your answer. I’m going to need you to speak up.” He teased the younger skeleton as he slowly pushed in a slender fingertip. Sans was so tight and perfect for the brilliant royal scientist.  
“Please! I need you to fuck me. I want it  
I’ve fantasized about this moment so many times…I..need you to..I..I..”  
Without much of a warning Gaster pushed in his tentacle cock, it filled him so much that the young skeleton could not help the tears that welled up in the corners of his eye sockets. Gaster had Sans writhing beneath the onslaught and his chest hit the surface of Gaster’s desk over and over again as moaned loudly. “You are so very loud Sans. It’s such a good thing that we are the only ones in the building.” Gaster pulled out almost entirely before he slammed back in Sans hole causing him to scream out Gaster’s name as he came untouched all over Gaster’s desk. The older scientist wasn’t very far behind him. He had lost his composure, his lust controlling his actions. His teeth scraped along San's collarbone, swearing loudly as he filled the younger skeleton with his cum. 

Sans slumped down onto the floor, blissful and happily spent. Gaster sat down beside him to pull his assistant into a warm embrace. “That was amazing.” Sans spoke softly against Gaster’s chest. “Yes it was. Next time I will be sure to treat you to dinner first.” Gaster said before pulling away from the younger skeleton to place a gentle kiss on his forehead.

**Author's Note:**

> Check out my undertail nsfw blog on Tumblr @funtimesinthevoid


End file.
